The present invention relates generally to RAID data storage systems and methods, and deals more specifically with a system and method for transferring data from a secondary storage controller to a storage media after failure of a primary storage controller for said storage media.
It was previously known that data security is improved by data redundancy such as provided by RAID. RAID (redundant array of independent disks) systems are well known today, and there are several levels of RAID. To implement one of the RAID levels, a plurality of storage controllers and storage media such as a hard disk drive are connected by a shared bus interface such as a parallel SCSI bus. Alternately, the plurality of storage controllers and storage media may be connected in a dual loop using Fiber Channel Arbitrated Loop shared bus protocol. An ATA shared bus interface is also known. The SCSI and Fiber Channel shared interfaces are typically used in applications requiring high reliability such as those involving a server. The ATA interface is typically used for less secure storage media such as those for a desktop personal computer. This is because the ATA interface is lower cost than the SCSI or the Fiber Channel the interface.
FIG. 17 is a view schematically showing a RAID system using the previously known ATA interface. As shown in FIG. 17, a storage controller 90 is connected to and manages a plurality of storage arrays 92 and 94. Each of the arrays 92 and 94 comprises one or more storage physical media 96 such as a hard disk. The controller 90 utilizes the ATA interface 98 to record/store data on the arrays 92 and 94. The ATA interface 98 is also coupled to a host computer 99 via a proper interface such as Fiber Channel, to exchange data with the host.
FIG. 18 is a block diagram showing in more detail the RAID system using the conventional ATA interface shown in FIG. 17. As shown in FIG. 18, the controller 90 includes a fiber channel connector 100, fiber channel-host protocol control means 102, a processor 104, and a cache memory 106 connected to the processor 104. The controller 90 communicates with another RAID system 101 or the host computer 99 via the fiber channel connector 100. Data received by the controller 90 is converted into a proper protocol via the protocol control means 102, and recorded in each of the storage media 96 having a proper address by the processor 104.
As shown in FIG. 18, the conventional ATA interface 98 is connected to each of the storage media 96 via suitable connection means 108, and manages these storage media 96, thus enabling data transfer between the host computer and each of the storage media via the ATA interface 98.
The ATA interface 98 may perform data transfer by use of a parallel transfer technology such as ATA/100 in view of its improved data transfer rate. Nevertheless, the ATA technology within ATA/100 has limitations. The following attempts have been made to improve the data transfer rate of the ATA. A data transfer rate having a clock frequency of 50 MHz and a maximum transfer rate of 100 Mbytes/s with a data width of 16 bits has been achieved for the ATA/100 interface. In order to further improve the data transfer rate, another attempt of doubling the data width to 32 bits or increasing a frequency of a strobe signal has been made. However, it has been known that the increase of the data width or the increase of the frequency of the strobe signal causes difficulties in data synchronization between signal lines, and significant interference/noise between the signal lines. Therefore, in the ATA interface, when the transfer rate of UltraDMAmode3 (44.4 Mbytes/s) or more is used, a connection with an 80 wire flat cable and 40 pins is used. Each pin is accompanied by a ground, and the interference between the signal lines is prevented.
In recent years, due to speedup in computer systems and an increase in the amount of data to be stored, the data transfer rate of the interface of the controller requires further improvement. Also, reliability of the data transfer from the storage controller to the storage media must be maintained. Also, the cost of the data storage system should be minimized despite the need for redundancy of data storage.
Such demands on the system will likely further increase, especially where the storage unit is separated from the server and connected to the server by the Fiber Channel as an independent storage area network (SAN), or in the case where the storage unit is connected to the server via the Ethernet(registered trademark) link for use.
Accordingly, an object of the present invention is to provide a high speed interface between the storage controller and redundant storage media.
Another object of the present invention is to provide such a high speed while maintaining a low cost and high reliability.